Prostate cancer (PCa) is the most frequently diagnosed malignancy in men worldwide, and the second leading cause of cancer death for men in the United States. Developing new PCa metabolomic biomarkers capable of predicting tumor aggressiveness can drastically improve PCa treatments and patient prognostications. Previous studies have indicated the utility of spermine as a potential biomarker for prostate cancer. However, quantifying spermine using in vivo MRS is difficult due to the overlapping chemical shifts of spermine with other metabolites in the spectra.We used LnDOTP^5-, a stable anionic lanthanide macrocyclic complex, to form a sufficiently stable ternary complex with positively charged spermine. The ion-pair interaction resulted in the selective shift of the spermine MR resonances in D₂O. The magnitude and direction of the shift is dependent on the pseudocontact contribution of the lanthanide (Ln). Here we report the affinity of different LnDOTP^5- complexes (Eu^III, Yb^III,and Tm^III) for spermine and the effect of complex formation on the spermine MR resonances in D₂O and serum solutions, as well as intact human prostate tissue, to best mimic physiological conditions. D2O and Serum Samples. Prepared samples of 10 mM spermine and 10 mM citrate in D₂O or serum were analyzed with MRS on a Bruker AVANCE spectrometer operating at 600 MHz (14.1T). D₂O was added to serum samples for field locking. Eu^III, Yb^III,and Tm^III complexes were evaluated at 4ºC. Intact Tissue. Frozen tissue was scanned using high-resolution magic angle spinning (HRMAS) MRS on the same Bruker spectrometer. A 4 mm zirconia rotor with Kel-F inserts created a 10 μl sample space for tissue samples, and D₂O was added for field locking. After an initial scan, 4 μl LnDOTP5- was added to one rotor and 4 μl of D₂O was added to another rotor as control. Both rotors were kept overnight at 4ºC and then rescanned the next day. Spectra were recorded at 4ºC with the spectrometer frequency set on the water resonance. Spectra were measured with HRMAS with a spin rate of 3600Hz (±1.0Hz), and analyzed using an in-house developed MatLab based program.In D_²O, spermine forms stable 1:1 complexes with LnDOTP^5- (K > 105 M-1) and the lanthanide-induced shift can be large, with shifts up to 100 ppm for the Tm^III complex at 37 ºC. In tissue, the spermine peaks were shifted, but the final locations were unknown (Figure 1). The resonances of citrate also disappeared, which was not seen in the control D₂O solution. We further investigated these phenomena with solutions of bovine serum. In serum solutions, an excess of the LnDOTP^5- is needed to achieve the maximum spermine shifts seen in a 1:1 ratio (LnDOTP^5-: spermine) in D₂O, suggesting other possible interactions with ions present within the serum, hence also probable in other physiological conditions (Figure 2). Further experiments, including the effects of cations and anions on the spermine shifts and the interactions between LnDOTP^5- and citrate have also been conducted, with results to be presented at the meeting.LnDOTP^5- shift agent successfully shifted spermine MR resonances downfield of the water peak in both D₂O and serum solutions. Spermine was also shifted away from its traditional resonance in tissue. The results of experiments exploring the effects of ions, such as Zn²⁺, Ca²⁺, and phosphate, as well as the observed shift of citrate in tissue, will enhance the understanding of the ion-pair interactions of spermine-LnDOTP^5- complex in physiological conditions. The use of LnDOTP^5- shift agents present as a possible noninvasive method for quantifying spermine and staging prostatic lesions, as well as a useful tool when combined with imaging techniques, such as CEST technology.